1. Field of the Invention
The present invention relates to transformer apparatuses configured with integrated inverter transformers and balance transformers, inverter transformers including coils for balance transformers, and drive circuits for driving them.
2. Description of the Related Art
It is a widely utilized technology to control currents flowing through a plurality of cold cathode discharge tubes to predetermined values in a cold cathode discharge tube drive circuit by connecting a balance transformer to a low voltage side of the drive circuit or by connecting a balance transformer to a high voltage side to which a cold cathode discharge tube is connected. It is known that in a cold cathode discharge tube, a voltage applied to electrodes of the cold cathode discharge tube fluctuates depending on an impedance fluctuation or the like, so that currents flowing through each cold cathode discharge tube is changed depending on the impedance of each cold cathode discharge tube.
As well-known, on backside of a liquid display panel, a plurality of cold cathode discharge tubes are installed as back-lights. As a recent trend, a size of a liquid display panel becomes larger. For example, an average size for a home-use liquid crystal TV has been changed to use a liquid crystal display panel of 32 to 45 inches from 20 inches.
As the size of the liquid crystal display panel becomes larger, the number of cold cathode discharge tubes used in one liquid crystal TV also increases. Therefore, if the currents flowing through each of the cold cathode discharge tubes are different to each other as described above, unevenness of emission occurs between cold cathode discharge tubes. This invites unevenness of luminance in a liquid crystal display panel, so that it is necessary to comfort currents flowing through installed all cold cathode discharge tubes for providing a high-quality liquid crystal TV. Therefore, it is common to use an inverter transformer and a balance transformer in a cold cathode discharge tube drive circuit.
In this case, conventionally, it has been proposed to connect a balance transformer coil to a low-voltage side or a high-voltage side in a cold cathode discharge tube drive circuit.
Further, an inverter transformer having a plurality of coils has been proposed so as to drive a plurality of cold cathode discharge tubes with a single magnetic path of the inverter transformer.
Sill further, such drive circuit has been proposed that an inductance element connected in series with a first primary coil and an inductance element connected in series with a second primary coil are provided in the same magnetic path.
Also, an inverter transformer configured with an IHI-shaped core portion has been proposed by the assignee of this application. Followings are patent documents related to the drive circuits and/or transformer apparatuses.
Japanese Patent Laid-open No. 2003-31383                Japanese Patent Laid-open No. 2004-506294        Japanese Patent Laid-open No. 2005-311227        Japanese Patent Laid-open No. 2004-349293        Japanese Patent Laid-open No. 64-030463        Japanese Patent Laid-open No. 2000-133531        
However, it is well-known that an inverter transformer and a balance transformer are separately produced as independent transformer. Accordingly, in case of assembling a cold cathode discharge tube drive circuit, an inverter transformer, a balance transformer, a switching circuit and a control circuit are generally mounted on a circuit board, independently. However, a separate mounting of an inverter transformer and a balance transformer on the circuit board requires an extra space, and further costs for parts and production also increase. In addition, it is hard to downsize the cold cathode discharge tube drive circuit, and it has become difficult to satisfy the request of downsizing and low-weighting from the liquid crystal display panel side.